Coupling between cyclooxygenases and prostaglandin F2α synthase: Detection of an inducible,glutathione-activated,membrane-bound prostaglandin F2α-synthetic activity

Distinct functional coupling between cyclooxygenases (COXs) and specific terminal prostanoid synthases leads to phase-specific production of particular prostaglandins (PGs). In this study, we examined the coupling between COX isozymes and PGF synthase (PGFS). Co-transfection of COXs with PGFS-I belonging to the aldo-keto reductase family into HEK293 cells resulted in increased production of PGF_2α only when a high concentration of exogenous arachidonic acid (AA) was supplied. However, this enzyme failed to produce PGF_2α from endogenous AA, even though significant increase in PGF_2α production occurred in cells transfected with COX-2 alone. This poor COX/PGFS-I coupling was likely to arise from their distinct subcellular localization. Measurement of PGF_2α-synthetic enzyme activity in homogenates of several cells revealed another type of PGFS activity that was membrane-bound, glutathione (GSH)-activated, and stimulus-inducible. In vivo, membrane-bound PGFS activity was elevated in the lung of lipopolysaccharide-treated mice. Taken together, our results suggest the presence of a novel, membrane-associated form of PGFS that is stimulus-inducible and is likely to be preferentially coupled with COX-2.